Histones
In order for DNA to be packaged tightly enough to fit into a chromosome, it wraps around proteins called Histones, located in the nucleus of a cell[1].
Histones can be organized into six classes:
1.H1
2.H2A
3.H2B
4.H3
5.H4
6. Archael
Witout histones, DNA would be too long to fit within the nucleus.
Some other functions of histones include acetlyation, methylation, ubiquitination, and phosphorylation[2].
References